返馳式轉換器之數位式初級側感測控制

Abstract

本論文針對返馳式轉換器之數位式初級側感測控制方法進行設計，可用於不連續導通模式之直流返馳式轉換器以及不連續導通模式、具功率因數修正之返馳式整流器。初級側感測方法可藉由輔助線圈來達到輸出電壓或電流的控制。然而，根據初級側感測誤差的分析，感測電壓會受到漏電感、線阻及次級側二極體壓降影響，因此，感測電壓只能達到有限的精準度。在不連續導通模式之直流返馳式轉換器的應用中，感測誤差可以藉由取樣時間調變來加以改善。透過取樣時間調變的方法，當負載大小從20%變化至100%時，輸出電壓在穩態時僅有1%的誤差且電壓壓降於切載時亦可控制在額定輸出電壓的4.7%。此外，將初級側感測方法用於不連續導通模式、具功率因數修正之返馳式整流器時，感測電壓在整流後輸入電壓接近零交越點時，因可供取樣的時間很短，不易取得正確的輸出電壓回授訊號。因此，採用多模式的控制演算法來克服此問題。當系統在整流後輸入電壓接近零交越點時，採用開迴路控制，而在其餘時間則採用預設的閉迴路控制。藉由此方法控制系統，輸入電流的總諧波失真在額定負載時僅有4.5%。在本論文中，利用一顆德州儀器公司的數位訊號處理晶片TMS320F2812來實現初級側感測控制方法。

This thesis presents the design and realization of primary-side sensing (PSS) technique for discontinuous-conduction-mode (DCM) DC-DC flyback converters or flyback rectifiers with power factor correction (PFC). PSS technique can be used for the output voltage or current regulation by employing an auxiliary winding. However, by analyzing the primary-side sensing error, the sensed voltage from the auxiliary winding may be corrupted by switching noise due to leakage inductance, winding resistance, and the voltage drop of the secondary diode, therefore the sensed voltage can only achieve limited accuracy. The sensing error can be improved by sampling instant modulation for DCM DC-DC flyback converters. The voltage regulation has only 1% deviation and the voltage drop is only 4.7% of the nominal output voltage when the load power is from 20% to 100%. When utilizing PSS technique for DCM PFC flyback rectifiers, the sensed voltage is difficult to be obtained at the neighborhood of zero crossing of the rectified input voltage. Therefore, a multimode control algorithm is implemented to overcome this problem. The system is under open-loop control at the neighborhood of zero crossing and closed-loop control when the correct sensed voltage is able to be obtained. By this method, the total harmonic distortion (THD) of the ac line current is only 4.5% at the rated output power. In this thesis, PSS technique is realized by a digital signal processor (DSP), TMS320F2812 from Texas Instrument (TI).